The new game apparently isn't anywhere close to release, however. Here's a statement from Eidos Montreal General Manager Stephane D'Astous:

Were in the early development stages for Thief 4, but this is an incredibly ambitious project and a very exciting one. It's too early for us to offer any specific game details, right now we are focused on recruiting the very best talent to join the core team at the studio and help us make, what we believe will be one of the most exciting games on the market.

A teaser site is up at thief4.com, showing a logo from the same school of awkward number-letter substitutions as the movie Se7en. That site links to the official forum, too. Despite the dearth of details, one would assume the sequel will bring back the steampunk-medieval setting and the same elaborate sneaking mechanics of its predecessors.

As Shacknews points out, Eidos Montreal is also working on another hotly anticipated sequel to a classic PC game: Deus Ex 3. Last year, the game's lead designer suggested the possibility of a PC-only release for that particular game.